1. Field of the Invention
The present invention relates to an apparatus and a method for controlling operation of a reciprocating compressor, and in particular to an apparatus and a method for controlling operation of a reciprocating compressor which are capable of improving an operational efficiency of a compressor by varying an operation frequency.
2. Description of the Prior Art
A general reciprocating compressor (hereinafter, it is referred to as a compressor) performs a reciprocating motion of a mover by supplying a sine wave voltage or a rectangular pulse wave voltage to a stator coil in turns and repeatedly applying a certain linear stroke to the mover. In more detail, when a serial current flows to the stator coil, the stator""s iron core is magnetized and turned into an electromagnet. Then, the mover made of an iron core and supporting an air gap with a bearing is magnetized and moved by a suction force. Next, when a current direction of the stator is changed, the operational direction of the suction force acting on the mover is changed, and the mover is moved into the opposite direction. As described above, if an excitation current direction of the stator is continuously changed by turns, the mover performs the reciprocating motion continually.
FIG. 1 is a block diagram illustrating a construction of a general apparatus for controlling operation of a compressor. As depicted in FIG. 1, the general apparatus includes a linear compressor 150 adjusting a freezing capacity by moving a piston up and down by a voltage applied to the compressor in accordance with a stroke reference value, a voltage detecting unit 130 detecting a voltage applied to the compressor 150 according to an increase of a stroke, a current detecting unit 120 detecting a current applied to the compressor 150 according to the increase of the stroke, a microcomputer 140 calculating a stroke by using the detected voltage and current, comparing the calculated stroke with a stroke reference value and outputting a control signal according to the comparison result, and an electric circuit unit 110 intermitting AC power to a triac according to the control signal of the microcomputer 140 and applying a voltage to the compressor 150.
In the compressor 150, because the piston moves up and down by a voltage applied according to the stroke reference value set by a user, a stroke can be varied, accordingly a freezing capacity can be adjusted.
The stroke increases by lengthening a turn-on cycle of the triac of the electric circuit unit 110 according to the control signal from the microcomputer 140. Herein, the voltage detecting unit 130 and the current detecting unit 120 respectively detect the voltage and the current applied to the compressor 150 and apply them to the microcomputer 140.
Then, the microcomputer 140 calculates a stroke by using the voltage and the current, compares the stroke with the stroke reference value and outputs a control signal according to the comparison result. In more detail, when the stroke is smaller than the stroke reference value, the microcomputer 140 increases a voltage applied to the compressor 150 by outputting a control signal for lengthening an on cycle of the triac, when the stroke is greater than the stroke reference value, the microcomputer 140 decreases a voltage applied to the compressor 150 by outputting a control signal for shortening the on cycle of the triac,
However, since the reciprocating compressor control apparatus according to the conventional art has a severe non-linearity in its mechanical motion characteristics, the operation of the reciprocating compressor can not be performed precisely and accurately by a linear control method without considering the non-linearity.
An operational efficiency of the compressor can be improved by controlling a phase difference between a current and a stroke uniformly, however when the compressor is continually operated, its operational efficiency may be lowered according to a load variation due to circumstances changes.
Accordingly, it is an object of the present invention to improve an operation efficiency of a compressor by controlling an operation speed constantly so as to place an operation point of the compressor within a high efficiency operation region by using a phase difference between a piston speed and a current and varying an operation frequency according to a load variation.
In addition, it is another object of the present invention to improve an operation efficiency of the compressor by controlling a TDC (top dead center) constantly so as to place an operation point of the compressor within a high efficiency operation region by using a phase difference between a piston speed and a current and varying an operation frequency according to a load variation.
In order to achieve the above-mentioned objects, an apparatus for controlling operation of a compressor includes a detecting means for detecting various elements related to an operation efficiency of a compressor; a phase difference comparing means for comparing phases of the elements each other and outputting a phase difference according to the comparison; an operation frequency determining means for determining a frequency at a certain time point as an operation frequency by increasing/decreasing a reference operation frequency by a certain frequency units according to the phase difference; an operation reference value determining means for determining an operation reference value according to the operation frequency outputted from the operation frequency determining means; and a control means for comparing the operation reference value with the elements detected by the detecting means, applying a control signal according to the comparison result to the compressor and varying an operation frequency of the compressor according to the operation frequency determined by the operation frequency determining means.
A method for controlling operation of a compressor includes operating a compressor with a reference frequency; determining a speed at an inflection point as a speed reference value after calculating the inflection point by using a phase difference between a piston speed of a compressor and a current applied to the compressor; operating the compressor according to the speed reference value; and varying an operation frequency of the compressor when a load variation occurs and varying the speed reference value according to the varied operation frequency.
A method for controlling operation of a compressor includes operating a compressor with a reference frequency; determining a TDC (top dead center) at an inflection point as a TDC reference value after calculating the inflection point by using a phase difference between a power voltage and a current; operating the compressor according to the TDC reference value; and varying an operation frequency of the compressor when a load variation occurs and varying the TDC reference value according to the varied operation frequency.